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Biointegrated Pintucci keratoprosthesis provides good functional results, surgeon says
For patients who are not candidates for penetrating keratoplasty, an artificial cornea may be the only possibility to restore vision.
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Keratoprostheses are generally made with an optical cylinder to allow images to be focused on a functioning retina, and with a supporting element to fix the device to the eye. The most important issue with implanting an artificial cornea is obtaining perfect biological, mechanical and functional anchorage of the device to eye tissues.
A study of the history of keratoprostheses (KP) made since 1879 shows that KP extrusion is mainly due to epithelial proliferation around the implant with the formation of retroprosthetic membranes. The supporting element must be made of a soft, pliable material, and must allow the passage of metabolites to ocular tissues. The supporting element also must be biologically integrated with the ocular tissues.
Since 1948, PMMA has been successfully used for the optical cylinders of KPs. Many materials, such as metal, plastic and ceramic, have been used for the KP supporting element without great success because they are not biologically integrated with the eye tissues and are not flexible enough to follow eye deformations. Biological materials such as dentin, bone, cartilage and homologous cornea are well tolerated but do not integrate with the eye and can be reabsorbed, leading to inflammatory rejection responses.
Biointegrated KP
After a decade of research in the field, I believe that the ideal supporting element must be made of a colonizable biomaterial without dangerous biological side effects such as necrosis. It also must avoid mechanical stresses that lead to inflammation, tissue melting, infection and extrusion of the device. Thus, we developed a new biointegratable KP in 1979, together with a unique implantation technique that has been constantly improved since then. The Pintucci KP can be implanted in thinned or perforated corneas, in corneas with stromal melting, and in eyes that have undergone several procedures including penetrating keratoplasty, other KP implantations, and glaucoma, cataract and vitreoretinal surgery.
The supporting element of the Pintucci KP is made of a biointegrated Dacron fabric skirt that allows three-dimensional colonization by newly formed vascularized connective tissue. This fabric is soft and pliable, can be easily cut into the desired shape and sutured, and is chemically inert and not subject to resorption. The Dacron fabric support is fixed to the PMMA optical cylinder with a specific reliable method (international patent pending).
The colonized KP prevents the epithelial downgrowth along the shaft of the optical cylinder by contact inhibition and by leaving no empty spaces at the implant-eye interface, therefore preventing retroprosthetic membranes, leakage and microbial contamination.
The colonized supporting element placed on the cornea has an excellent biological and mechanical function for which it is covered with an autologous oral mucosal graft. The oral mucosal graft is extremely suitable because of its faster cellular turnover than the superior lid skin and conjunctiva employed in other KPs.
Functional and anatomical conditions of the eye, conjunctiva and lids must be studied carefully. Often reconstructive plastic surgery is necessary prior to the KP implant. In dry eyes, the oral mucosal graft must be protected by tarsorrhaphy.
Two-stage procedure
For the first surgical stage, general anesthesia with nasal intubation is preferred.
In order to colonize the Pintucci KP, it is implanted in the inferior lid. A l5-mm incision of the skin is performed in the orbitopalpebral sulcus. Then the orbicular muscle fibers are spread apart to the orbitopalpebral septum, creating a pocket. The KP to be colonized is introduced upside down in the pocket. The orbicular muscle and the skin are sutured. The patient is medicated as usual for plastic surgery. The KP is left in place for about 45 days, the time necessary for good colonization of the Dacron material.
If trichiasis, entropion or symblepharon are present, palpebral and conjunctival plastic procedures are performed. If lacrimal secretion is reduced, the lacrimal puncta are closed with diathermy. To expose the eye, two lid traction sutures are applied. The corneal epithelium is then completely removed.
A free oral mucosal graft is cut from the lower lip. If the conditions of the lower lip mucosa are not good, we cut the graft from the superior lip or from the cheek. To stop bleeding, homeostatic forceps are employed, and a l:3,000 epinephrine solution is injected.
It is important to note that buccal mucosa is employed to cover the colonized biointegrated Dacron felt and, if necessary, to cover deficiencies in the palpebral and bulbar conjunctiva. Once it is removed from the mouth, the buccal mucosal free graft shortens in diameter by a third. The size and the shape of the mucosal graft are marked with gentian violet dots. No suturing of the donor site is required after cutting the graft. The wound heals satisfactorily, and more grafts may be taken from the same area at a later date. Fine hooks or sutures are used to raise the cut edge while it is being dissected from submucosal tissue.
After removal, the graft is stretched over the surgeon's left forefinger and excess submucosal fat is dissected away with fine scissors. The mucosa is washed and kept in a balanced salt and gentamicin solution. The oral mucosa is applied to the corneal surface and sutured into place. Blood clots are removed. Antibiotic ointment is applied, and the lids are closed. A dressing, as well as a protective plastic shield, is applied over the operated eye.
Second stage
After at least 45 days, which is necessary for good Dacron felt colonization of the KP and for the oral mucosal graft to heal, the second surgical stage may be performed under general anesthesia.
Eye hypotony is obtained with 250 cc intravenous mannitol, and an oculopressor is applied. The colonized KP is removed from the inferior lid, and the orbicular muscle and skin are sutured. Excessive connective tissues and the fibrous membrane that covers the PMMA optical cylinder are removed. The KP is checked under the operating microscope, and the fixation of the optical part is tested.
The KP is stored in a sterile glass vial with some drops of balanced salt solution with gentamicin. In order to protect the oral mucosal membrane, especially in dry eyes, we reduce the length of the palpebral fissure with a lateral and nasal tarsorrhaphy, leaving a central aperture for the optical cylinder. In eyes with normal tear secretion, we prefer smaller tarsorrhaphies or we divide them when indicated. Given that the tarsorrhaphy procedure causes compression of the eye, we prepare it before KP implantation.
The oral mucosal graft is inspected and the eye is prepared for surgery.
The cornea is exposed (Figure 1), partially dissecting the oral mucosal graft starting from the supratemporal sector up to the center of the cornea. Once the cornea is exposed, the KP optical cylinder zone is marked with a circular marker.
A diamond knife is used to make three partial-thickness radial incisions in the 2-, 6- and l0-o'clock meridians. The center of the cornea is trephined with a suitable corneal trephine, and the radial incisions are completed with scissors (Figure 2).
To perform iridodialysis, the iris is cut and drawn down to the 6-o'clock direction; then with lateral movements it is completely removed. After 1.5 minutes the anterior chamber is irrigated with balanced salt solution to stop bleeding, and the blood clots are removed.
Extraction of the lens is performed.
The posterior part of the optical cylinder is introduced into the anterior chamber (Figure 3), and the colonized supporting flange and the radial incisions are sutured. Air is injected in the anterior chamber; blood clots around and behind the colonized supporting flange are removed in order to obtain good healing of the colonized KP.
The oral mucosa is sutured and trephined in the center to allow the passage of the anterior part of the optic (Figure 4). In dry eyes, tarsorrhaphies are sutured and antibiotic ointment is applied. The dressing and a protective plastic shield are applied over the operated eye.
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Images: Pintucci S |
Vision immediately restored
In the last 21 years, the Pintucci KP has been implanted in 1,128 eyes in Europe, Asia, India and Africa, under different socioeconomic conditions. The indications extend from vascularized leukomas to keratomalacia, trachoma, corneal ulcerations, septic infections, leprosy, ocular pemphigoid, Stevens-Johnson and Leyle syndromes, rosacea keratitis, herpetic keratitis and dry eye syndrome. Studies of different groups of etiologies show significantly different outcomes: chemical burns have the best probability of success, which is related to relatively healthy intraocular structures.
The incidence of postoperative glaucoma is low. Factors such as age, sex or previous surgery have no influence on outcome. KP oral mucosal necrosis is the principal complication observed in dry eyes, in autoimmune diseases and in ocular pemphigoid (85% of 128 Italian patients); multiple additional surgeries were often required.
Functional results have been successful. More than half of the patients obtained enough visual acuity to be independent, and nearly one-quarter of them improved to 20/30 or better. Visual field is not limited because of the improved Pintucci KP optics.
The Pintucci KP has overcome many of the difficulties presented by mechanical anchorage and biointegratability of keratoprostheses.
For Your Information:
- Stefano Pintucci, MD, can be reached at Oftalma, via Bruxelles 59, Rome 00198, Italy; 39-06-8411884; fax: 39-06-8559271. Dr. Pintucci has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.